Mario Rando MEng COIIM

The Samuel Beckett Bridge, Dublin Citys newest bridge, is now established as a landmark movable structure spanningthe maritime gateway to the city. The bridge is located east of the citys centre and within the heart of the newlydeveloped docklands area, facilitating an important urban transport link for private car use, public transport, cyclistsand pedestrians; and contributing towards the improved environmental, commercial and social development of theurban area in which it is located. The bridge is a Calatrava-designed, cable-stayed, steel box girder structure, with aspan, across the River Liffey, of 123 m. The bridge, which rotates through 90 , has an asymmetric shape reflecting thatof a harp laid on its side, with the base to the cable-stayed steel pylon set outside of the rivers navigational channel 28 m from the rivers south quay wall. The pylon curves northwards to a point 46 m above the water level with 25forestay cables set in a harp formation. This paper describes the basis of the bridges structural and operationaldesign, and the manner in which the main river support was constructed, and the superstructure fabricated andpositioned.

1.

Introduction

The Samuel Beckett Bridge, Dublin Citys newest bridge, is

now established as a landmark structure spanning themaritime gateway to the city. The bridge is located east ofthe citys centre and within the heart of the newly developeddocklands area, facilitating an important urban transport linkfor private car use, public transport, cyclists and pedestrians;and contributing towards the improved environmental,commercial and social development of the urban area inwhich it is located.The design brief for the bridge sought to achieve a landmarkstructure of unmistakable modernity and unique character thatwould act as a symbol for the city and a catalyst for futuredevelopment in the area. At the concept design stage a numberof ideas were examined, but the one that best met the clientsrequirements was the concept of a bridge similar in form to theCeltic Harp, the harp being of significance as it is a symbol ofIreland (see Figure 1).

The Dublin Docklands Master Plan (Dublin Docklands

Development Authority, 1997) required that all future bridgeswithin the area have opening spans in order to facilitate thecontinued movement of shipping and to maintain the amenityof the river.In 1999, Dublin City Council, the client for the project, appointedSantiago Calatrava as designer for the bridge crossing. Calatravasbrief was to provide a signature bridge design for the river crossinglocation together with a design for the bridges approach roads.Calatrava appointed a local firm, Roughan and ODonovan, toassist with the civil aspects of the bridge design, together withpreparing the contract and tender documentation.

The Samuel Beckett Bridge is a cable-stayed, steel box girder

Samuel Beckett Bridge, Dublin,

IrelandCutter, Flanagan, Brown, Randoand Mo

The cross-section of the deck consists of two pedestrian and

cycle tracks and four lanes for vehicular traffic, two of whichcan be adapted to accommodate trams in the future. Thecable-stays are all locked coil cables with twenty-five 60 mmdiameter cables supporting the front span and a total of six145 mm diameter cables towards the back. The main supportin the river consists of bored concrete piles, with a concrete pilecap supporting a circular concrete pier of varying diameter.This houses the hydraulic turning and lifting equipment andthe horizontal and vertical bearings, which support the entirebridge while turning. At each end of the bridge, locking pinsare moved by hydraulic cylinders and locked into theabutments to enable the bridge to carry traffic (Table 1).

2.2

Structural layout and design

As the Samuel Beckett Bridge is a swing bridge, two main

conditions needed to be designed for(a)(b)Figure 1. Irish coin with harp symbol

bridge, which rotates through 90 to maintain shipping

movements upstream, has an asymmetric shape, with the baseto the cable-stayed steel pylon set outside of the rivers centralnavigation channel. The pylon curves northwards to a point46 m above the water level with 25 forestay cables set in aharp formation. An elevation of the bridge is shown inFigure 2.

the bridge in the open position, with no vehicular

loading and no support at the endsthe bridge in the closed position, subject to live loadingsand support at the embankments (see Figure 3).

The bridge was designed such that both of these conditions arefully satisfied, while ensuring that a fully balanced optimumweight solution was developed in order to facilitate an efficientoperation. The balance of the bridge in the open position thatis, minimal net moment at the main support is achieved bymeans of prescribing the mass of the counterbalance, withspecified tensions for the fore and backstays, in order toachieve the required profile of the deck and to align the bridge46 m

Table 1. Basic dimensions and data

correctly at the abutments. Using the variables of counterbalance, mass and cable tensions allowed the control of thedeck level and also minimised the axial force, bending momentand deflection of the pylon and deck. Once this balance was

achieved for the open condition the bridge could be analysed in

the closed position with full live load.2.2.1 Deck designThe main fore deck structure, the front span, is a multi-cellbox girder, made up from relatively thin steel plates stiffenedinternally using a combination of longitudinal bulb flats, anglesections and trapezoidal stiffeners. Cantilevered from this mainbox section are the ribs and steel decking, which form thepedestrian and cycle tracks (see Figure 4). The top of the boxconsists of a 14 mm thick plate with 12 mm trapezoidalstiffeners. The 36 mm mastic asphalt layer was taken accountof in the fatigue check for this orthotropic deck.The back span, which houses the counterbalance, is also amulti-cell box girder but made up from unstiffened steel

Fore stay anchorage

Future light rail

Crossgirder

Centralbox

External boxCrossgirder

Figure 4. Section through front span

plates. The cells in the back span were generally to be filled

with a combination of lead shot and concrete, which alsosupports the top and bottom plates, preventing them frombuckling locally. The ballast material was subsequentlychanged by the contractor to a combination of steel blocksand heavyweight concrete (see section 4.1.3). In order toachieve the final bridge balance the amount of steel ballastplaced on site during construction in these cells wasadjustable. This allows for the addition or removal of massin order to balance any future changes made to thesuperimposed dead loads on the bridge.An important structural and aesthetic feature of the bridge isthe single, central, line of forestays supporting the main spanfrom a curved pylon. Such an arrangement tends to lead tolarge torsional forces in the deck due to unbalanced liveloadings either side of the line support. Therefore, anadvantage of using a multi-cell box section is its inherenttorsional rigidity.2.2.2 SupportsThe bridges vertical support is provided by the main supportpier in the river and the locking pins at each abutment.The main support was originally designed in steel, but at thestart of the construction stage it was changed to concrete afteracceptance of a proposal made by the contractor (see section4.1.1).The main support sits on a large pile cap in the river; it has anouter diameter of 8?6 m at the base and 15?0 m at the top, andsupports the entire bridge when the bridge is turning, or whenin the open position. When the bridge is either fully open orclosed, the bridge sits on the outer rim of the main support, onan elastomeric bearing. When it is turning, the bridge is lifted75 mm off the rim bearing by hydraulic lifting cylinders. A10 m long central steel tube with a diameter of 2?5 m, and aplate thickness of 120 mm, welded to the superstructure below136Downloaded by [] on [01/12/15]. Copyright ICE Publishing, all rights reserved.

the base of the pylon, transfers the entire bridge load to the pilecap. The vertical load of 5850 t is transferred to the liftingcylinders at the main vertical bearing at the bottom of thecylinder (on top of the pile cap), and any out-of-balancemoment is taken by two horizontal bearings encircling thecentral steel tube 5?35 m apart. The main support also housesthe two hydraulic turning cylinders, which are working (due tolimited space available) as a pushpull system. Figure 5 showsan illustration of the bridges rotation mechanism within thebridges main support pier.The pile cap in the river, below the main support, wasoriginally designed as a 1661664 m heavily reinforced pilecap. Its thickness was later reduced to 3 m as part of thechange to a concrete support. The pile cap is supported byeighteen 1?2 m diameter bored cast-in-place piles, each with acapacity of 9500 kN.At the ends of the bridge hydraulically controlled locking pinsattach the bridge structure to the housings cast into theabutments. The locking pins are designed as part of the bridgerotation mechanism and provide the final alignment of thebridge, vertically and horizontally. This is necessary due to therange of deflections at the bridge ends such as temperatureeffects and cable sag.The abutments are reinforced concrete structures founded onbored concrete piles as shown in Figure 6.2.2.3 Cable arrangementThe front deck section spans between the main support and thenorth abutment. The central line of forestays effectivelybehaves as a row of vertical spring supports for the frontspan. Due to the inclination of these forestays, the stay forceshave significant horizontal components along the deck, whichare resisted by the deck structure acting in compression andbalanced by an equal and opposite force in the back span,provided by the force at the backstays.

Figure 6. South abutment (plan view and section)

Samuel Beckett Bridge, Dublin,

because of a large proportion of permanent loads and a small

proportion of varying loads, the designer and the independentchecker agreed to increase this to 53% of the MBL.

the start date. This allowed all those becoming involved withthe project the opportunity to absorb and understand theproject requirements and to consider where savings in time,cost and other risks could be produced. Several of the resultantvalue engineering options are discussed in section 4.1 below.

2.2.4 Pylon design

Each of the forestays is attached to the curved, inclined andslender pylon. This was fabricated from shaped and weldedthick steel plates, forming a variable box section. The pylon inturn transmits the applied cable reactions, by means of axialforces mainly, but also bending moments, to its base where it isfully connected to the main deck and the central liftingcylinder, and to its apex where it is restrained by the sixinclined backstays. These backstays also provide the necessarytransverse restraint of the pylon tip. The pylon, if simplified,can be considered as an arch, supported at the bottom and top,with an approximately uniform load from the forestays.The entire superstructure was modelled using finite-elementanalysis, in which the pylon was checked for buckling. Thepylon is restrained from buckling in the longitudinal directiondue to its arched shape and by the forestays, but is slender inthe transverse direction between the top and bottom where it isrestrained by the backstays and deck structure.

3.

Procurement

Following the detailed design and development of draft tender

documentation, Flint & Neill was appointed by Dublin CityCouncil to undertake a procurement stage review of theproposed scheme. This process was instigated by the client toprovide them with an independent expert view of the projectbefore the seeking of tenders. The review encompassed a widerange of headings covering procurement strategy, tender andcontract documentation, selection of tenderers, elements forcontractor design, constructability, tender review process andconstruction supervision options. The brief also required anindependent estimate of the outturn cost and the optimumcontract period. The review produced a range of suggestionsand recommendations, which, when implemented, gave theclient a much greater level of confidence to proceed with thescheme.As part of the procurement stage review, it was established thatpotential tenderers would need to pre-qualify by demonstratingan ability to meet a range of criteria pertinent to this project.The steel fabrication cost element was approximately 65% ofthe total cost of the project and as such it was considered thatthe client should have a direct contractual link to thefabricator.

After the contract had been awarded, but before work

commenced on site, the contractor proposed some alternativesolutions that would provide savings to the client, improve theprogramme and sequencing of the work, reduce risk duringconstruction and offer maintenance benefits over the lifetimeof the bridge.4.1.1 Main supportThe contractor proposed to change the main pier from steel toconcrete as shown in Figure 7. The client required the externalappearance and profile of the pier to remain as it was andalthough it would be difficult to form it in concrete, the contractorfelt that it was less complex than having to fabricate it in steel. Inaddition, the concrete pier offered the following advantages.(a)

(b)(c)

(d)The successful tenderer was a joint venture between theNorthern Ireland contractor, Graham, and the Dutch fabricator, Hollandia. There then followed an extended periodbefore the formal award of contract and the establishment of

Construction

Construction works on the 30-month contract commenced on

site in May 2007. The civil and marine aspects of the projectwere carried out concurrently with the fabrication of the steelsuperstructure and the development of the bridges rotationmechanism. The project works were supervised by theengineers team, in which the engineer and the engineersrepresentative were client (Dublin City Council) in-houseappointments, as were the resident engineering staff for thecivils aspects of the works. Flint & Neill were engaged withinthe engineers team in providing the resident engineering stafffor the steelwork. In order to deal with design-related queriesand for technical approval of the contractors proposals, adesigners representative position was created in the engineersteam, which was filled by a Calatrava engineer.

(e)

There would be significant long-term maintenance

benefits in the marine environment as no painting orcathodic protection would be required over the lifetime ofthe structure. It was felt that concrete offered a moresustainable solution for the marine environment.The concrete pier would be less prone to damage fromfloating debris or river traffic.Constructing the pier in concrete eliminated the need forsea transportation of the large steel sections and the needfor a large floating crane to lift them in.It meant that the pier could be constructed at an earlierstage of the project, improving the work sequence andremoving the activity from the critical path.Because of the ground conditions the contractor wantedto minimise the depth of the pile cap to ensure stability of

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IrelandCutter, Flanagan, Brown, Randoand Mo

Turning cylinders

10 m

Concrete structure

Steel tube welded to deck

3m

Lifting cylinders

Pile cap

Figure 7. Main river support structure in concrete

Figure 8. Samuel Beckett Bridge

the cofferdam (see section 4.2). Changing the pier from

steel to concrete enabled the contractor to redesign thepile cap and reduce its thickness from 4 m, which wasrequired for the steel pier, to 3 m.4.1.2 Ship impact protection pilesThe entire bridge is protected against the possibility of shipimpact in its open position, and the central pier is protectedwhen it is closed. This was to be achieved using ship impactprotection piles as shown in Figures 3 and 8.The piles had originally been designed using a simple method toresist an impact from the largest vessel, which uses this part ofthe Port of Dublin only a few times a year. The contractorcarried out a more detailed probabilistic analysis in which theannual probability of the bridge collapsing as a result of a shipimpact is compared with an acceptable target probability. Thevessel movement data were obtained from the Dublin Portauthorities and the ship impact analysis was carried out inaccordance with the AASHTO guide specification for vesselcollision design of highway bridges (AASHTO, 1991). Thebridge was designed for a target probability of 0?001, equivalentto a theoretical period between catastrophic vessel collisionaccidents of 1000 years. The result of this was to optimise thediameter of the piles, which meant that they could beconstructed using conventional floating plant and piling rigs.The above contractors proposals were accepted by the clienton the basis that the contractor became responsible for thealternative designs for the various elements.4.1.3 Ballast materialsAt the tender stage, the materials specified to provide thenecessary counterweight to balance the bridge were lead shotand concrete. At that time the price of lead, quoted at theLondon Metals Exchange, had been rising markedly and wascontinuing to increase. Significant increased costs could beavoided if the balance of the bridge could be achieved usingalternative materials.The contractor developed a proposal to replace the lead andconcrete ballast material with the alternative combination ofsteel blocks and heavyweight concrete with a density of3?9 t/m3 using magnetite aggregate.4.1.4 Superstructure erectionThe bridge steel superstructure, including the bridge deck andpylon, was initially planned to be assembled and erectedalongside the rivers quay wall, over the supporting pier, on atemporary platform in the river with individual sections liftedinto place using a heavy lift marine crane. It was envisagedwithin the tender documentation that once the bridge superstructure was complete the falsework could be removed allowing140Downloaded by [] on [01/12/15]. Copyright ICE Publishing, all rights reserved.

Samuel Beckett Bridge, Dublin,

IrelandCutter, Flanagan, Brown, Randoand Mo

the balanced structure to rest on the supporting pier. However,

on examination of this proposed method, the contractorconsidered an alternative method entailing the assembly of thecomplete bridge superstructure within Hollandias fabricationfacility in Rotterdam and transportation by sea to Dublin. Thisalternative method was proposed to the engineer, who on carefulexamination accepted the proposal. There were clear advantagesin the alternative proposal, particularly relating to the increasedquality of workmanship that would be possible by fabricatingthe superstructure within the fabrication facility, and theresultant reduced environmental impact of the works on theconfined urban site.

4.2

Construction of main support

One of the most significant challenges faced on site was the

construction of the river pier. Following the value engineeringexercise referred to in section 4.1, the pier now consisted of a15615 m hexagonal base, 3 m deep, with a 10 m highcylindrical stem widening at the top to provide support tothe superstructure. It was supported on eighteen 1200 mmdiameter bored cast-in-place concrete piles, each socketed intothe rock beneath.Immediately following award of the contract, the contractorcarried out an additional site investigation around the area ofthe pier to supplement the investigation previously carried outat the preliminary design stage. The construction of the piernecessitated a 20 m square sheet piled cofferdam, and theadditional site investigation provided more detailed information on the level of the rock-head, the permeability of the rockand the properties of the overburden material. It revealed thatbelow the underside of the proposed pile cap, there would beless than 3 m of firm to stiff clay overlying limestone/mudstone, which was weathered and fractured in places. Thisraised the possibility of water pressure in the rock exerting anuplift on the underside of the clay, such that it could cause thebase of the cofferdam to heave.Tony Gee and Partners were engaged by the contractor tocarry out the design of the cofferdam. AZ46 sheet piles weredriven to the top of the bedrock before the levels of walers andstruts were progressively installed as the cofferdam wasdewatered. Before the cofferdam could be completely dewatered, the silt had to be removed and concrete tremmied intoplace to act as a bottom strut. Pressure relief wells wereinstalled to avoid the excess build-up of pressure in the rockunderneath, with piezometers also installed to monitor thepressure at various locations across the base. Predeterminedparameters were specified by the contractors designer to allowwork to take place safely within the cofferdam. The pressurerelief wells proved to be effective and the piezometers indicatedthat the pressure under the base remained at safe levels duringconstruction.

Bridge EngineeringVolume 164 Issue BE3

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IrelandCutter, Flanagan, Brown, Randoand Mo

Figure 9. Pile construction within cofferdam

The installation of the foundation piles for the pier pile capprovided a particular challenge as the underside of the pile capwas approximately 13 m below high water level. The contractor elected to lift the piling rig into the base of the cofferdamand install the bored piles from there (see Figure 9).This gave the piling rig greater control over the installation ofthe piles compared with installing them from a platform abovehigh water level. It also meant that the piles could be installedmuch more quickly and safely.Figure 10. Bespoke formwork for quadrant of main support

The top section of the pier was complex in its geometry, withthe outside surface curving in two planes. Bespoke formworkwas designed and assembled and the concrete was cast inquarters see Figure 10.Due to the numerous interfaces with the mechanical andelectrical works, considerable liaison was needed to ensureeverything was cast in to the required tolerances. The largestcast-ins, each weighing approximately 2?5 t were for connection to the main turning cylinders near the top of the pier.All power and telemetry cables had to enter the bridge bymeans of the main pier as it was the point about which thebridge would rotate. Eight 120 mm diameter ducts were castinto the pier base and turned up the inside of the pier.Following removal of the cofferdam, they were laid in a trenchin the river bed and up through the south quay wall near thebridge control room.

4.3

Rotation system

The rotation system was specified as a contractor-designed item

with a performance specification provided by the designer. Theprinciple for allowing the bridge to be rotated by 90 consists ofensuring that the centre of gravity of the bridge (without live

load) is positioned centrally within the main support pier. A

series of five hydraulic jacks lift the central steel pipe to raise thebridge, weighing 5850 t, 75 mm off the main rim support; thepipe passes through two levels of horizontal ring bearings withinthe pier and is seated on a low friction bearing. Once lifted, twolarge hydraulic rams rotate this tube, and hence the bridge,through 90 . The design uses a system with one pushing and onepulling cylinder (see Figure 5).The bridge, when in use by traffic, sits on the continuoushorizontal ring bearing on the rim of the river support pierwith a pair of locking pins at each end of the bridge insertedinto housings cast into the abutments; these pins locate thebridge to the required position and level. An expansion joint isprovided at each end of the bridge formed by movable steelboxes, which are pushed by hydraulic rams against the face ofthe abutments; by allowing the pressure in these hydraulic ramsto vary, the bridge can expand and contract. When the bridgeis required to rotate, the pressure in the rams is reversed, theboxes withdraw from the abutment faces and the locking pinsare withdrawn into the bridge structure, leaving the structurefree to be lifted and rotated.141

Samuel Beckett Bridge, Dublin,

Figure 11. Backstay anchorage deck section being transported to

assembly area

Figure 12. The fulcrum bridge deck section during fabrication

The electrical control cabinets, hydraulic tanks and electrical

pump units are all located within the bridge deck structureclose to the base of the pylon to limit the effect of their weighton the balance of the bridge.Electrical power to the bridge is provided from the south sideof the river by means of the underwater ducts into the mainsupport pier. An emergency generator is provided within thebridge control building in case the mains supply fails.

4.4

Fabrication and assembly

The size of the individual elements to be fabricated was

dictated by the facilities at Hollandias workshops. The size,weight and shape of sections were dictated by the amount ofhandling necessary and the unit size that could be accommodated in their painting facility. The contractor determinedthat the bridge deck should be made up of eight sections andthat these, once painted, would be joined together on aprepared assembly area where the completed unit could beeasily transferred onto a seagoing barge for transport toDublin.The deck section weights for structural steelwork varied from160 t for the typical front span section up to 510 t for the backstayanchorage deck section, excluding ballast see Figure 11.The pylon was fabricated in five sections; the base section wasprefabricated and fitted to the bridge deck and the remaining foursections were welded together, lifted, positioned and temporarilysupported while the final circumferential welds were laid.A range of welding processes were used during fabrication,with each method selected to suit the joint configuration andposition. Automated processes such as submerged arc wereused whenever possible but with manual methods, mainly flux142Downloaded by [] on [01/12/15]. Copyright ICE Publishing, all rights reserved.

core, also being used extensively. All butt welds and a

proportion of fillet welds were examined using ultrasonicmethods for buried defects and magnetic particle inspection forsurface breaking defects.Figure 12 shows deck section 3 during fabrication. It is thisunit that sits on the rim support and is lifted by the central tubewhen the bridge is required to rotate.

4.5

Superstructure transport and erection

At the outset, the contractor investigated the maximum unit

size that could be delivered to the site; the only viable methodwas by sea, but each unit would need to pass along the riverfrom Hollandias fabrication yard to the east of Rotterdam tothe sea and then be able to pass through the East Link Bridgein Dublin. The East Link Bridge was found to be the limitingwidth restriction and the Konigshaven Bridge in Rotterdamgave the height limit. A detailed follow-up investigationidentified that if some railings and street furniture could betemporarily removed from the East Link Bridge it would bepossible for the complete bridge superstructure, includingpylon and stays, to pass through on a suitable tide level.Detailed planning and analysis was undertaken by thecontractor on the technical aspects of transferring the superstructure onto a sea barge and the fastening and ballastingrequirements for the subsequent voyage (see Figure 13).The superstructure, weighing approximately 2500 t at thisstage, was shipped to Dublin in May 2009. The journey fromRotterdam to Dublin was carefully monitored throughout the1005 km journey. This took 8 days to complete as the shipmentwas forced to shelter from high winds for a period beforetraversing the Irish Sea (see Figures 14 and 15).Following arrival in Dublin, with the bridge still supported onthe barge and now moored to the quay wall, it was necessary to

Bridge EngineeringVolume 164 Issue BE3

Samuel Beckett Bridge, Dublin,

IrelandCutter, Flanagan, Brown, Randoand Mo

Figure 13. Bridge superstructure being transferred onto barge

Figure 15. Bridge passing through East Link Bridge, Dublin

ballast the back span to ensure the centre of gravity was

located centrally within the support zone. The structure wasthen skidded along the seagoing barge to a position thatallowed the backstay end to be supported on a second barge,thus leaving the bridge support area free above the river. Thebridge lifting cylinder had been positioned within the mainsupport pier and would later be welded to the main structure.

position, the final welded connection of the bridge lifting

cylinder was made and the hydraulic system connected andtemporarily activated to rotate the bridge to span the river forthe first time.

With the bridge now balanced and supported on two barges,

their moorings were released and at high tide the barges weremoved so as to position the bridge support area directly abovethe pier that had been cast in the river. Temporary guides hadbeen welded to the bridge lifting cylinder to ensure that as thetide receded, the bridge would be lowered onto the rim supportat the precise required position (see Figure 16). Once this hadbeen achieved, and as the tide level continued to reduce, thebarges could be moved away from the bridge, leaving thestructure balanced and supported on the rim bearing. Once in

Figure 14. Bridge on barge, being towed across the Irish Sea

4.6

Geometry control

Following the initial rotation of the bridge the cables were

tensioned to a predetermined level and the bridge supported ontemporary jacks at the locking pin locations. This allowed thereactions at the end supports to be monitored and theinformation fed back to the design model to allow revisedstay forces to be calculated.While fabricating and assembling the bridge in Rotterdam, thecontractor had started the site works on the abutments.However, these abutments could not be completed until thebridge was positioned, as it was necessary to ensure that thebridge behaved as predicted and would fit perfectly between

Figure 16. Bridge, supported on two barges, being placed onto

Samuel Beckett Bridge, Dublin,

IrelandCutter, Flanagan, Brown, Randoand Mo

the abutments. Once the bridge was in place, any moderate

discrepancy in bridge deflection due to permanent loads wascompensated for by a change to the levels at the abutments.Strict control of densities and volumes was specified, but sometolerance had to be allowed for. Some adjustment was allowedfor in the cable forces, but as already described, the backstayshad already been taken to the maximum acceptable level andany change that caused an increase of backstay forces couldnot be allowed.

The completed bridge is already recognised as a structure of

unmistakable modernity acting as a symbol for the City ofDublin, and has attracted much positive publicity fromresidents and from visitors to the Irish capital.

During the construction of the bridge the designers finiteelement model was continuously updated to take account ofthe densities, volumes and weights reported by the contractor.A significant amount of reanalysis was required at this stage toachieve a good balance between final cable forces and bridgedeformations. When cable forces were changed to amend thedeformation of the ends of the deck, stresses in the bridgestructure changed accordingly and had to be checked. Theback span of the bridge is extremely stiff, while the pylon andfront span deform relatively easily. This resulted in a complexequation with numerous variables, which was finally solved byamending levels at the abutments, ballast quantities and cableforces.

4.7

Completion

Once the bridge was in its closed position, the top surface of thedeck was shot-blasted and waterproofed before the concretekerbs and medians were constructed using lightweight concretein the fore span and heavyweight concrete in the back span. Thecarriageways were surfaced with 36 mm thick mastic asphalt.The finishing works were then completed on the adjacentquays including roadworks, a granite-clad control roombuilding and reinstatement of the masonry quay walls. Theproject was completed on programme in a period of 30months. Samuel Beckett Bridge was opened by the LordMayor of Dublin on 10 December 2009. A photograph of thecompleted bridge is shown in Figure 8.

5.

Conclusion

The delivery of this iconic bridge was a major challenge to all

the parties involved and was achieved not only through closecooperation and respect between client, designer, technicaladvisors and the contractor, but also by the ability andcommitment of the craftsmen and operatives tasked with itsproduction.Due to the complexity of the bridge, the engagement of anindependent project reviewer before tendering the projectproved to be valuable, as was the period of time available tothe contractor for value engineering in advance of workcommencing on site.144Downloaded by [] on [01/12/15]. Copyright ICE Publishing, all rights reserved.

Commentary for Vessel Collision Design of Highway

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